The present invention relates to endoscopes, and, in particular, provides an endoscope that can be safely sterilized in an autoclave.
Endoscopes typically include a plurality of concentric tubes which define passages for a set of lenses and for bundles of optical fibers. The optical fibers carry light which illuminates the lenses and allows the user to view a desired part of the body. One or both ends of the endoscope may include windows, although one of the lenses can comprise a window. The windows provide a hermetic seal against the outside environment. The tubes defining the endoscope are usually rigid, and can be made of stainless steel.
In the prior art, it has been known to use adhesives to mount the lenses and/or the windows to the tube. Epoxies or other organic materials are commonly used to hold the lenses in place within the endoscope, to attach the windows to the ends of the tube, and/or to hold the optical fibers in position. But epoxies and other adhesives have the disadvantage that they deteriorate when exposed to heat and steam.
An autoclave is the preferred device for sterilizing an endoscope. But an autoclave generally produces temperatures in the range of about 270.degree. F. After repeated exposure to the heat of an autoclave, the epoxy seals tend to deteriorate and fail. A mismatch in the coefficient of expansion between the endoscope wall and the lenses and windows can cause the endoscope tube to rip away from the epoxy. Optical fibers held in place by epoxy may become loose or even break due to deterioration of the epoxy. As a result, what is intended to be a hermetic seal becomes less than hermetic.
Epoxies and other adhesives also evaporate when subjected to heat. When one heats and then cools a conventional endoscope, the evaporated material will condense on the lenses, forming a film which becomes thicker after repeated cycles of heating and cooling. Thus, an additional disadvantage of a conventional endoscope is that, after repeated autoclaving cycles, the optical transmissivity of its lenses decreases so much that the endoscope must be replaced.
The present invention provides an endoscope which has no adhesives or epoxies whatever. By avoiding such materials, one can build an endoscope which suffers no harm in an autoclave, even after repeated thermal stress.